Method for forming silicon nitride film selectively on sidewalls or flat surfaces of trenches

ABSTRACT

A method for fabricating a layer structure in a trench includes: simultaneously forming a dielectric film containing a Si—N bond on an upper surface, and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the film formed on the upper surface and the bottom surface and a sidewall portion of the film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage between two electrodes between which the substrate is place in parallel to the two electrodes; and substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the film by wet etching which removes the one of the top/bottom portion and the sidewall portion of the film more predominantly than the other according to the different chemical resistance properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/048,422, filed Feb. 19, 2016, the disclosure of which is herein incorporated by reference in its entirety. The applicant/inventors herein explicitly rescind and retract any prior disclaimers or disavowals made in any parent, child or related prosecution history with regard to any subject matter supported by the present application.

BACKGROUND

Field of the Invention

The present invention relates generally to a method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate.

Related Art

In manufacturing processes of large-scale integrated circuits (LSIs), there are several processes for forming sidewalls in trenches. The sidewalls are used as spacers or used for blocking etching of a structure from side surfaces of trenches. Conventionally, the sidewalls were formed by forming a conformal film on surfaces of trenches, and then removing portions thereof formed on an upper surface in which the trenches were formed and portions formed on bottom surfaces of the trenches by asymmetrical etching. However, when such a formation method is used, over-etching is required in order to remove footing of sidewalls in which the thickness of the sidewalls increases near and at the bottom, forming a slope. Over-etching causes etching of an underlying layer and causes damage to a layer structure.

Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.

SUMMARY

In some embodiments, a film formed on a top surface of a substrate in which a trench is formed and on a bottom surface of the trench and a film formed on the sidewalls of the trench possess different film properties associated with wet etching (i.e., directional control of film properties). By subjecting the substrate to wet etching, it is possible to remove selectively either the film formed on the top/bottom surface of the trench or the film formed on the sidewalls of the trench, i.e., selectively forming either a film extending in a horizontal direction or a film extending in a vertical direction in a trench structure. According to the above method, a horizontal or vertical layer in a trench structure can selectively be formed solely by wet etching without dry etching as an etching means (i.e., directional control of film formation).

In some embodiments, the film having directionally controlled film properties can be a silicon nitride film deposited by plasma-enhanced chemical vapor deposition (PECVD) or plasma-enhanced atomic layer deposition (PEALD). Alternatively, in some embodiments, a silicon nitride film is deposited without directional control, and then the film is treated to provide directionality of film properties. That is, when ion bombardment is exerted on a silicon nitride film during deposition of the film or after the deposition of the film, impurities can be removed from the film, thereby causing densification of the film and improving the film quality; however, when ion bombardment is intensified and asymmetrically exerted on the dielectric film in a direction perpendicular to the film, the film quality is degraded, thereby dissociating Si—N bonds, decreasing the density of the film, and increasing wet etching rates. The above phenomena are totally unexpected since generally ion bombardment is believed to cause densification of a film and to decrease the wet etch rate. The intensity of ion bombardment can be directionally controlled by a plasma generated using a parallel plate electrode configuration, e.g., a capacitively coupled plasma, which can control the incident direction of ions, the dose of ions, and the energy of ions. Based on the above principle which is not intended to limit the invention, the directionality of film properties can be controlled.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a protective film usable in an embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supply system using a flow-pass system (FPS) usable in an embodiment of the present invention.

FIG. 2 is a flowchart illustrating steps of fabricating a layer structure according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating steps of fabricating a layer structure according to another embodiment of the present invention.

FIG. 4 is a flowchart illustrating steps of fabricating a layer structure according to still another embodiment of the present invention.

FIG. 5 is a flowchart illustrating steps of fabricating a layer structure according to yet another embodiment of the present invention.

FIG. 6 is a flowchart illustrating steps of fabricating a layer structure according to a different embodiment of the present invention.

FIG. 7 is a graph showing the relationship between RF power and wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench, showing a threshold (reference) RF power, according to an embodiment of the present invention.

FIG. 8 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of silicon nitride films formed according to embodiments of the present invention.

FIG. 9 shows a Scanning Electron Microscope (SEM) photograph of a cross-sectional view of a silicon nitride film formed according to an embodiment of the present invention.

FIG. 10 illustrates a cross-sectional view of a silicon nitride film formed according to an embodiment of the present invention.

FIG. 11 illustrates a cross-sectional view of a silicon nitride film formed according to another embodiment of the present invention.

FIG. 12 is a graph showing the relationship between RF power and Si—N peak intensity [au] of a SiN film according to an embodiment of the present invention.

FIG. 13 is a graph showing the relationship between RF power and density [g/cm³] of a SiN film according to an embodiment of the present invention.

FIG. 14 is a graph showing a general relationship between plasma density and wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench according to an embodiment of the present invention.

FIG. 15 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of silicon nitride films formed according to embodiments of the present invention.

FIG. 16 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of silicon nitride films formed according to other embodiments of the present invention.

FIG. 17 shows Scanning Electron Microscope (SEM) photographs of cross-sectional views of silicon nitride films formed according to still other embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a precursor gas and an additive gas. The precursor gas and the additive gas are typically introduced as a mixed gas or separately to a reaction space. The precursor gas can be introduced with a carrier gas such as a noble gas. The additive gas may be comprised of, consist essentially of, or consist of a reactant gas and a dilution gas such as a noble gas. The reactant gas and the dilution gas may be introduced as a mixed gas or separately to the reaction space. A precursor may be comprised of two or more precursors, and a reactant gas may be comprised of two or more reactant gases. The precursor is a gas chemisorbed on a substrate and typically containing a metalloid or metal element which constitutes a main structure of a matrix of a dielectric film, and the reactant gas for deposition is a gas reacting with the precursor chemisorbed on a substrate when the gas is excited to fix an atomic layer or monolayer on the substrate. “Chemisorption” refers to chemical saturation adsorption. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a noble gas. In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers.

In this disclosure, “containing a Si—N bond” may refer to being characterized by a Si—N bond or Si—N bonds, having a main skeleton substantially constituted by a Si—N bond or Si—N bonds, and/or having a substituent substantially constituted by a Si—N bond or Si—N bonds. A dielectric film containing a Si—N bond includes, but is not limited to, a SiN film and a SiON film, which have a dielectric constant of about 2 to 10, typically about 4 to 8.

In this disclosure, “annealing” refers to a process during which a material is treated to get into its stable form, e.g., a terminal group (such as an alcohol group and hydroxyl group) present in a component is replaced with a more stable group (such as a Si-Me group) and/or forms a more stable form (such as a Si—O bond), typically causing densification of a film.

Further, in this disclosure, the article “a” or “an” refers to a species or a genus including multiple species unless specified otherwise. The terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. Also, in this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

Additionally, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments. However, the present invention is not limited to the preferred embodiments.

Some embodiments provide a method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate, comprising: (i) simultaneously forming a dielectric film containing a Si—N bond on the upper surface, and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage between two electrodes between which the substrate is place in parallel to the two electrodes; and (ii) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching which removes the one of the top/bottom portion and the sidewall portion of the dielectric film more predominantly than the other according to the different chemical resistance properties. The term “simultaneously forming” may refer to forming generally or substantially at the same time, in the same process, or in the same step, which includes depositing generally or substantially at the same time, in the same process, or in the same step, and/or treating generally or substantially at the same time, in the same process, or in the same step. In this disclosure, the term “substantial” or “substantially” may refer to ample, considerable, or material quantity, size, time, or space (e.g., at least 70%, 80%, 90%, or 95% relative to the total or referenced value) recognized by a skilled artisan in the art to be sufficient for the intended purposes or functions.

FIG. 2 is a flowchart illustrating steps of fabricating a layer structure according to an embodiment of the present invention. Step S1 and step S2 correspond to steps (i) and (ii), respectively. In step S1, by using plasma bombardment, a dielectric film having directionality of film properties is formed over a trench. The plasma bombardment can be applied during the deposition of the film or after the completion of deposition of the film. In step S2, according to the difference in the film properties between the top/bottom portion of the film and the sidewall portion of the film, one of the portions of the film is more predominantly etched than the other by wet etching, leaving only one of the portions in the layer structure.

In step S2, the wet etching is conducted using a solution of hydrogen fluoride (HF), for example.

By adjusting bombardment of a plasma excited by applying voltage between two electrodes between which the substrate is place in parallel to the two electrodes, a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls can be given different chemical resistance properties. A plasma is a partially ionized gas with high free electron content (about 50%), and when a plasma is excited by applying AC voltage between parallel electrodes, ions are accelerated by a self dc bias (V_(DC)) developed between plasma sheath and the lower electrode and bombard a film on a substrate placed on the lower electrode in a direction perpendicular to the film (the ion incident direction). The bombardment of a plasma can be represented by plasma density or kinetic energy of ions (ion energy). The plasma density can be modulated mainly by tuning the pressure and RF power (the lower the pressure and the higher the power, the higher the plasma density becomes). The plasma density can also be modulated by applying a dc bias voltage or an AC voltage with a lower frequency set for ions to follow (<1 MHz). The plasma density can be determined using a probe method (e.g., “High accuracy plasma density measurement using hybrid Langmuir probe and microwave interferometer method”, Deline C, et al., Rev. Sci. Instrum. 2007 November; 78(11): 113504, the disclosure of which is incorporated by reference in its entirety). When inserting a probe in a plasma and applying a voltage thereto, an electric current flows through the probe, which is called “ion saturation current” (I_(i)) which can be calculated as follows, and then the plasma density (N_(p)) can be calculated as follows: I _(i) =e×N _(e)√(kT _(e) /M)×exp(½)eA; N _(p) =I _(i)√(M/kT _(e))/exp(½)eA, wherein I_(i): ion saturation current [A]; A: surface area of the probe [m²]; e: electronic charge [C]; Ne: electron density [m⁻³]; k: Boltzmann's constant [J/K]; T_(e): electron temperature [K]; M: ion mass [kg].

FIG. 14 is a graph showing a general relationship between plasma density and wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench according to an embodiment of the present invention. In this graph, the chemical resistance properties are represented by wet etch rate. On the top/bottom surface of the film, plasma bombardment is exerted generally in a direction perpendicular to the film surface, whereas on the sidewall surface of the film, plasma bombardment is exerted generally in a direction parallel to the film surface. The wet etch rate of a film formed on the top/bottom surfaces of a trench is low when the plasma density is low since ions included in the plasma exerted on the film remove impurities and cause densification of the film. However, the wet etch rate of the film formed on the top/bottom surfaces increases as the plasma density increases as shown in FIG. 14, because the dose of ions is so high as to enhance dissociation of Si—N bond. On the other hand, the wet etch rate of a film formed on the sidewall surfaces of the trench is high when the plasma density is low since the dose of ions included in the plasma exerted on the film is insufficient to remove impurities and to cause densification of the film. However, the wet etch rate of the film formed on the sidewall surfaces decreases as the plasma density increases as shown in FIG. 14. In other words, the film quality of the film formed on the top/bottom surfaces is degraded as the plasma density increases, whereas the film quality of the film formed on the sidewall surface is improved as the plasma density increases. Thus, there is a threshold point in the plasma density where the film quality (or film characteristics) of the film on the top/bottom surfaces and that of the film on the sidewall are substantially equivalent, i.e., the line showing the relationship between plasma density and the wet etch rate of the film formed on the top/bottom surfaces and that of the film formed on the sidewalls intersect at the threshold point as shown in FIG. 14. The film characteristics of the film on the top/bottom surfaces and that of the film on the sidewall surface are reversed at the threshold point. Accordingly, by adjusting the plasma density, the film having directionality of film properties can be formed. When the plasma density is set to be lower than the threshold point, the film on the sidewalls can be more predominantly removed than is the film on the top/bottom surfaces by wet etching, whereas when the plasma density is set to be higher than the threshold point, the film on the top/bottom surfaces can be more predominantly removed than is the film on the sidewalls by wet etching. Accordingly, a desired layer structure can be fabricated.

In FIG. 14, the intersecting point (threshold point) is changed according to the duration of application of voltage, the frequency, the pressure, the distance between the electrodes, the temperature, etc., wherein, generally, the longer the duration of application of voltage, and the lower the pressure, the lower the plasma density at the intersecting point becomes. It should be noted that when the pressure, RF power, voltage, etc. are constant, a relationship substantially similar to that shown in FIG. 14 can be obtained between wet etch rate and RF power between parallel electrodes. The threshold point can be determined prior to steps (i) and (ii) based on this disclosure and routine experimentation. Thus, in some embodiments, the method for fabricating a layer structure further comprises, prior to steps (i) and (ii), repeating the following steps to determine the threshold point (reference point): (a) simultaneously forming a dielectric film under the same conditions as in step (i) except that the voltage is changed as a variable; and (b) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching under the same conditions as in step (ii).

FIG. 3 is a flowchart illustrating steps of fabricating a layer structure according to an embodiment of the present invention. Step S11 corresponds to steps (a) and (b), and steps S12 and S13 correspond to steps (i) and (ii), respectively. In step S11, the threshold voltage for plasma bombardment for reversing film characteristics of a top/bottom portion and a sidewall portion of a film is determined. In step S12, by using plasma bombardment at a voltage adjusted with reference to the determined threshold voltage, a dielectric film having directionality of film properties is formed over a trench. For example, when a voltage higher than the threshold voltage is applied between the electrodes in step S12, the wet etch rate of the top/bottom portion of the film becomes higher than that of the sidewall portion of the film, resulting in predominantly removing the top/bottom portion of the film, rather than the sidewall portion of the film by wet etching in step S13. On the other hand, when a voltage lower than the threshold voltage is applied between the electrodes in step S12, the wet etch rate of the sidewall portion of the film becomes higher than that of the top/bottom portion of the film, resulting in predominantly removing the sidewall portion of the film, rather than the top/bottom portion of the film by wet etching in step S13.

When ion bombardment is exerted on a film without using a parallel electrode configuration, e.g., by using a reactant in low-pressure chemical vapor deposition (LPCVD), a threshold point such as that shown in FIG. 14 would not be obtained since the reactant in LPCVD does not create asymmetrical ion bombardment, i.e., does not create directionality of film properties. For example, United States Patent Application Publication No. 2003/0029839 discloses LPCVD in which nitrogen-containing ions such as N₂ ⁺ are implanted to form a nitrogen-enriched layer, followed by thermal annealing to promote Si—N and N—H bonds in the layer so as to reduce the wet etch rate of the layer. In contrast, in some embodiments of the present invention, asymmetrical plasma bombardment using nitrogen is exerted on a top/bottom layer, which does not enrich nitrogen in the layer, but dissociates Si—N bonds and reduces the density of the layer, thereby increasing the wet etch rate of the layer formed on the top/bottom surfaces, relative to the wet etch rate of the layer formed on the sidewalls of a trench. In the above, when Si—N bonds are dissociated, Si dangling bonds and N dangling bonds are formed, which are ultimately terminated by hydrogen, forming N—H bonds and Si—H bonds. As a result of dissociating Si—N bonds, the density of the layer is decreased, and the wet etch rate is increased. Thus, in some embodiments, no thermal annealing (such as at 900° C.) is conducted between steps (i) and (ii) in order to avoid densification of the top/bottom layer (i.e., to avoid reducing the wet etch rate of the top/bottom layer). Further, in some embodiments, the incident energy of ions is less than approximately 200 eV (plasma potential is approximately 100 to 200 V), which is lower than that disclosed in United States Patent Application Publication No. 2003/0029839 (0.5 to 20 keV). As with the reactant in LPCVD, a reactant in thermal atomic layer deposition (ALD) and a plasma of remote plasma deposition do not form a threshold point such as that shown in FIG. 14 since the plasmas of thermal ALD and remote plasma deposition also do not create asymmetrical ion bombardment, i.e., do not create directionality of film properties. Further, when a plasma such as surface wave plasma (SWP) having low electron temperature and low ion kinetic energy of incident ions is used, the effect of ion bombardment is very limited, and thus, film degradation does not occur, and thus, it is difficult to create directionality of film properties. Furthermore, even when plasma bombardment is exerted on a film constituted by silicon oxide, the film quality of the silicon oxide film is not degraded, and thus, it is difficult to create directionality of film properties.

In some embodiments, the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes. Further, in some embodiments, inductively coupled plasma (ICP), electron cyclotron resonance (ECR) plasma, microwave surface wave plasma, helicon wave plasma, etc. can be used as the plasma, wherein bias voltage is applied to the electrodes as necessary to increase dc bias voltage between the plasma and electrode.

In some embodiments, the RF power is higher than the reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the wet etching removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film.

In some embodiments, the plasma is a plasma of Ar, N₂, and/or O₂ or other atoms which have an atomic number higher than hydrogen or helium.

In some embodiments, the trench has a width of 10 to 50 nm (typically 15 to 30 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is 10 to 50 nm), a depth of 30 to 200 nm (typically 50 to 150 nm), and an aspect ratio of 3 to 20 (typically 3 to 10).

In some embodiments, the dielectric film can be used as an etching stopper, low-k spacer, or gap-filler. For example, when only the sidewall portion is left, the portion can be used as a spacer for spacer-defined double patterning (SDDP), or when only the top/bottom portion is left, the portion can be used as a mask used for solid-state doping (SSD) of a sidewall layer exclusively.

In some embodiments, step (i) comprises: (ia) placing a substrate having a trench in its upper surface between the electrodes; and (ib) depositing the dielectric film on the substrate by plasma-enhanced atomic layer deposition (PEALD) using nitrogen gas as a reactant gas, wherein the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes in each cycle of the PEALD, wherein the RF power is higher than the reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent so that the wet etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film. In the above, the film having directionality of film properties is formed as the film is depositing, not after the completion of deposition of the film.

FIG. 4 is a flowchart illustrating steps of fabricating a layer structure according to still another embodiment of the present invention. Step S21 corresponds to step (ib), and step S22 corresponds to step (ii). In step S21, a dielectric film having directionality of film properties is deposited over a trench by using plasma bombardment at a voltage higher than the threshold voltage, and in step S22, a top/bottom portion of the film is more predominantly removed than is a sidewall portion of the film, so that substantially only the sidewall portion is left in the layer structure.

In some embodiments, step (i) comprises: (ia) placing a substrate having a trench on its upper surface between the electrodes; and (ic) depositing the dielectric film on the substrate by plasma-enhanced atomic layer deposition (PEALD) using nitrogen gas as a reactant gas, wherein the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes in each cycle of the PEALD, wherein the RF power is lower than reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent so that the wet etching in step (ii) removes the sidewall portion of the dielectric film selectively relative to the top/bottom portion of the dielectric film. In the above, the film having directionality of film properties is formed as the film is depositing, not after the completion of deposition of the film.

FIG. 5 is a flowchart illustrating steps of fabricating a layer structure according to yet another embodiment of the present invention. Step S31 corresponds to step (ic), and step S32 corresponds to step (ii). In step S31, a dielectric film having directionality of film properties is deposited over a trench by using plasma bombardment at a voltage lower than the threshold voltage, and in step S32, a sidewall portion of the film is more predominantly removed than is a top/bottom portion of the film, so that substantially only the top/bottom portion is left in the layer structure.

In some embodiments, the dielectric film is SiN film or SiON film or other Si—N bond-containing film.

In some embodiments, the PEALD or other deposition methods uses one or more compounds selected from the group consisting of aminosilane, halogenated silane, monosilane, and disilane as a precursor. The aminosilane and halogenated silane include, but are not limited to, Si₂Cl₆, SiCl₂H2, SiI₂H₂, bisdiethylaminosilane, bisdimethylaminosilane, hexaethylaminodisilane, tetraethylaminosilane, tart-butylamonosilane, bistart-butylamonosilane, trimehylsilyldiethylamine, trimethysilyldiethylamine, and bisdimethylaminodimethylsilane.

In some embodiments, step (i) comprises: (iA) depositing a dielectric film on a substrate having a trench in its upper surface; (iB) placing the substrate between the two electrodes; and (iC) exciting the plasma between the electrodes to treat a surface of the deposited dielectric film without depositing a film, wherein the plasma is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes, wherein the RF power is higher than the reference RF power at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent so that the wet etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film. In the above, the film having directionality of film properties is formed after completion of deposition of a film, by treating the film. In the above, step (ii) is post-deposition treatment which need not be cyclic.

FIG. 6 is a flowchart illustrating steps of fabricating a layer structure according to a different embodiment of the present invention. Step S41 corresponds to step (iA), step S42 corresponds to steps (iB) and (iC), and step S43 corresponds to step (ii). In step S41, a dielectric film is deposited over a trench, which film need not have directionality of film properties, although it can already possess directionality of film properties. In step S42, plasma bombardment as post-deposition treatment is exerted on the film at a voltage higher than the threshold voltage so that the wet etch rate of a top/bottom portion of the film is higher than that of a sidewall portion of the film. In step S43, the top/bottom portion of the film is more predominantly removed than is the sidewall portion of the film by wet etching, so that substantially only the sidewall portion of the film is left in the layer structure. Since the film is already deposited before the post-deposition treatment, the use of a voltage lower than the threshold voltage may not be effective because the wet etch rate of the sidewall portion does not become higher than that of the as-deposited film by exerting plasma bombardment on the film as illustrated in FIG. 14 discussed above.

In some embodiments, the deposited dielectric film has a thickness of approximately 10 nm or less (typically approximately 5 nm or less). If the film to be treated is thicker than approximately 10 nm, plasma bombardment does not reach a bottom of the film, i.e., it is difficult to adjust the wet etch rate of the film entirely in the thickness direction.

The dielectric film subjected to the post-deposition treatment can be deposited on the substrate by any suitable deposition methods including plasma-enhanced atomic layer deposition (PEALD), thermal ALD, low-pressure chemical vapor deposition (PCVD), remote plasma deposition, PECVD, etc. Preferably, the dielectric film is deposited by ALD since ALD can provide a high conformality such as more than approximately 70% (or more than 80% or 90%).

In some embodiments, no annealing is conducted after depositing the dielectric film and before step (ii).

In some embodiments, the plasma in step (i) is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes, wherein plasma density is higher than reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the wet etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film. As discussed above in relation to FIG. 14, the wet etch rate of a film formed on a top surface and that of a film formed on sidewalls of a trench can be adjusted by changing the plasma density, and the plasma density can be modulated mainly by tuning the pressure and/or RF power (the lower the pressure and/or the higher the power, the higher the plasma density becomes), and/or by applying RF power having a low frequency (<1 MHz).

In some embodiments, the plasma density is modulated by tuning the pressure in the reaction space, wherein the plasma density increases by lowering the pressure. In that case, the method further comprises, prior to steps (i) and (ii), repeating the following steps to determine the reference plasma density: (a) simultaneously forming a dielectric film under the same conditions as in step (i) except that the pressure is changed as a variable; and (b) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching under the same conditions as in step (ii).

In some embodiments, the pressure in step (i) is controlled below 350 Pa, including 300 Pa, 250 Pa, 200 Pa, 150 Pa, 100 Pa, 50 Pa, and 10 Pa, and any values between any two of the foregoing values.

In some embodiments, the plasma density is modulated by tuning a ratio of high frequency RF power to low frequency RF power constituting the RF power, wherein the plasma density increases by decreasing the ratio. In some embodiments, the high frequency RF power has a frequency of 1 MHz or higher (e.g., 10 MHz to 60 MHz), and the low frequency RF power has a frequency of less than 1 MHz (e.g., 200 kHz to 800 kHz). In the above, the method further comprises, prior to steps (i) and (ii), repeating the following steps to determine the reference plasma density: (a) simultaneously forming a dielectric film under the same conditions as in step (i) except that the ratio is changed as a variable; and (b) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching under the same conditions as in step (ii).

In some embodiments, the ratio of high frequency RF power (HRF) to low frequency RF power (LRF) is 0/100 to 95/5 (e.g, 10/90 to 90/10). In some embodiments, the RF power consists of the low frequency RF power. In some embodiments, the total RF power is 100 W to 600 W for a 300-mm wafer (which power is applicable to any size of wafer as wattage per area, i.e., 0.14 W/cm² to 0.85 W/cm²).

In some embodiments, any one or more of the variables discussed in this disclosure can be used to manipulate the plasma density when depositing a dielectric film so as to control selective etching in the etching process.

In the above embodiments where the ratio of HRF/LRF is controlled, low pressure and high RF power are not required as a variable to manipulate the plasma density when depositing a dielectric film, thereby making the process conditions less restricted. Further, in the embodiments, abnormal discharge by applying high RF power can be avoided.

In other embodiments where the wet etching in step (ii) removes the sidewall portion of the dielectric film selectively relative to the top/bottom portion of the dielectric film, plasma density is set lower than reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent.

In some embodiments, the deposition cycle may be performed by PEALD, one cycle of which is conducted under conditions shown in Table 1 below.

TABLE 1 Conditions for Deposition Cycle Substrate temperature 100 to 600° C. (preferably 250 to 550° C.) Pressure 10 to 2000 Pa (preferably 100 to 800 Pa); Less than 350 Pa (preferably 250 Pa or less) for WER of top/bottom being higher than WER of sidewall Precursor SiI₂H₂, etc. Precursor pulse 0.05 to 10 sec (preferably 0.2 to 1 sec) Precursor purge 0.05 to 10 sec (preferably 0.2 to 3 sec) Reactant N₂ + H₂ mixture, or NH₃ + N₂ mixture Flow rate of reactant 100 to 20000 sccm (preferably (continuous) 1000 to 3000 sccm) for N₂; 0 to 6000 sccm (preferably 0 to 600 sccm) for H₂ or NH₃ (H₂/N₂ = 0-0.5, preferably 0-0.2) Flow rate of carrier 100 to 5000 sccm (preferably gas (continuous) 1000 to 3000 sccm) Ar or N₂ Flow rate of dilution 0 to 10000 sccm (preferably 0 gas (continuous) to 5000 sccm) Ar or N₂ RF power Less than 600 W (preferably 100 (13.56 MHz) to 500 W) for WER of 300-mm wafer sidewall being higher than WER of top/bottom; 600 W or more (preferably 600 to 1000 W) for WER of top/bottom being higher than WER of sidewall A ratio of HRF/LRF Over 95/5 (typically 100/0) for WER of sidewall being higher than WER of top/bottom; 0/100 to 95/5 (preferably 0/100 to 90/10) for WER of top/bottom being higher than WER of sidewall RF power pulse 0.05 to 30 sec (preferably 1 to 5 sec) Purge 0.05 to 10 sec (preferably 0.2 to 3 sec) Growth rate per cycle 0.02 to 0.06 nm/cycle (on top surface) Step coverage (side/top; 20 to 100%; 30 to 100% side/bottom) (preferably, 50 to 100%; 50 to 100 %) Distance between 5 to 30 mm (preferably electrodes 7 to 20 mm) (numbers are approximate)

In some embodiments, the post-deposition treatment may be performed under conditions shown in Table 2 below.

TABLE 2 Conditions for Post-Deposition Treatment Thickness of 2 to 15 nm SiN film (preferably 5 to 10 nm) Substrate 25 to 600° C. temperature (preferably 100 to 500° C.) Pressure 10 to 2000 Pa (preferably 100 to 500 Pa) Reactant N₂, H₂, NH₃ Flow rate of 100 to 20000 sccm (preferably reactant 1000 to 3000 sccm) for N₂; (continuous) 0 to 6000 sccm (preferably 0 to 600 sccm) for H₂ or NH₃ (H₂/N₂ = 0-0.5, preferably 0-0.2) Flow rate of 100 to 5000 sccm carrier gas (preferably 1000 (continuous) to 3000 sccm) Ar or N₂ Flow rate of 0 to 10000 sccm dilution gas (preferably 0 to 5000 sccm) (continuous) Ar or N₂ RF power More than 600 W (13.56 MHz) for a (preferably 600 to 300-mm wafer 1000 W) Duration of RF power 1 to 600 sec. application (preferably 30 to 180 sec.) Distance between 5 to 30 mm electrodes (preferably 7 to 20 mm) (numbers are approximate)

In the above, no precursor is fed to the reaction chamber, and a carrier gas flows continuously.

In some embodiments, wet etching may be performed under conditions shown in Table 3 below.

TABLE 3 Conditions for Wet etching Etching solution HF 0.05-5% Etching solution 10 to 50° C. temperature (preferably 15 to 30° C.) Duration of 1 sec to 5 min etching (preferably 1 to 3 min) Etching rate 0.1 to 5 nm/min (preferably 0.5 to 2 nm/min) (numbers are approximate)

For wet etching, any suitable single-wafer type or batch type apparatus including any conventional apparatuses can be used. Also, any suitable solution for wet etching including any conventional solutions, such as phosphoric acid, can be used.

In some embodiments, in place of wet etching, any other suitable etching such as dry etching or plasma etching can be conducted. A skilled artisan can readily determined the etching conditions such as temperature, duration, etchant concentration, as routine experimentation in view of this disclosure.

In some embodiments, an insulation film can be formed only on a sidewall of a trench as follows:

1) forming a SiN film over a substrate having a trench pattern, in which a pulse of feeding a precursor and a pulse of exposing the substrate to an ambient atmosphere containing nitrogen species excited by a plasma are repeated, in which the plasma is excited in a manner exerting plasma bombardment on the substrate in a direction perpendicular to the substrate (the incident angle of ions is perpendicular to the substrate) under conditions such that the wet etch rate of a sidewall portion of the film is lower than that of a top/bottom portion of the film; and

2) removing the top/bottom portion of the film by wet etching.

In the above process sequence, the precursor is supplied in a pulse using a carrier gas which is continuously supplied. This can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching the main line and the detour line. FIG. 1B illustrates a precursor supply system using a flow-pass system (FPS) according to an embodiment of the present invention (black valves indicate that the valves are closed). As shown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber (not shown), first, a carrier gas such as Ar (or He) flows through a gas line with valves b and c, and then enters a bottle (reservoir) 30. The carrier gas flows out from the bottle 30 while carrying a precursor gas in an amount corresponding to a vapor pressure inside the bottle 30, and flows through a gas line with valves f and e, and is then fed to the reaction chamber together with the precursor. In the above, valves a and d are closed. When feeding only the carrier gas (noble gas) to the reaction chamber, as shown in (b) in FIG. 1B, the carrier gas flows through the gas line with the valve a while bypassing the bottle 30. In the above, valves b, c, d, e, and f are closed.

The precursor may be provided with the aid of a carrier gas. Since ALD is a self-limiting adsorption reaction process, the number of deposited precursor molecules is determined by the number of reactive surface sites and is independent of precursor exposure after saturation, and a supply of the precursor is such that the reactive surface sites are saturated thereby per cycle. A plasma for deposition may be generated in situ, for example, in an ammonia gas that flows continuously throughout the deposition cycle. In other embodiments the plasma may be generated remotely and provided to the reaction chamber.

As mentioned above, each pulse or phase of each deposition cycle is preferably self-limiting. An excess of reactants is supplied in each phase to saturate the susceptible structure surfaces. Surface saturation ensures reactant occupation of all available reactive sites (subject, for example, to physical size or “steric hindrance” restraints) and thus ensures excellent step coverage. In some embodiments the pulse time of one or more of the reactants can be reduced such that complete saturation is not achieved and less than a monolayer is adsorbed on the substrate surface.

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1A, for example. FIG. 1A is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas (and noble gas) and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a dilution gas is introduced into the reaction chamber 3 through a gas line 23. Further, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and surface treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere. In some embodiments, a remote plasma unit can be used for exciting a gas.

In some embodiments, in the apparatus depicted in FIG. 1A, the system of switching flow of an inactive gas and flow of a precursor gas illustrated in FIG. 1B (described earlier) can be used to introduce the precursor gas in pulses without substantially fluctuating pressure of the reaction chamber.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed close to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics, and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.

In some embodiments, an insulation film can be formed only on a sidewall of a trench as follows:

1) forming a SiN film over a substrate having a trench pattern (the film may or may not have directionality of film properties);

2) treating the film with a plasma excited in a manner exerting plasma bombardment on the substrate in a direction perpendicular to the substrate (the incident angle of ions is perpendicular to the substrate) under conditions such that the wet etch rate of a sidewall portion of the film is lower than that of a top/bottom portion of the film; and

3) removing the top/bottom portion of the film by wet etching.

EXAMPLES Example 1

A SiN film was formed on a Si substrate (Φ0300 mm) having trenches by PEALD, one cycle of which was conducted under the conditions shown in Table 4 (deposition cycle) below using the PEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substrate was subjected to wet etching under the conditions shown in Table 4 below.

TABLE 4 Conditions for Deposition Cycle Substrate temperature 400° C. Pressure 350 Pa Precursor SiI₂H₂ Precursor pulse 0.3 sec Precursor purge 0.5 sec Reactant N₂ Flow rate of reactant 2000 sccm (continuous) Flow rate of carrier 2000 sccm N₂ gas (continuous) Flow rate of dilution 0 sccm gas (continuous) RF power (13.56 MHz) Variable for a 300-mm wafer (see FIG. 7) RF power pulse 3.3 sec Purge 0.1 sec Growth rate per cycle 0.05 nm/cycle (on top surface) Number of cycles 200 times (10 nm) (thickness of film on top surface) Step coverage (side/top; 100%; 100% side/bottom) Trench depth/width (nm) 100/33 (AR = about 3) Distance between 15 mm electrodes Conditions for Wet etching Etching solution 0.5% HF Etching solution 20° C. temperature Duration of etching 2 min Etching rate Variable (see FIG. 7) (numbers are approximate)

The results are shown in FIG. 7. FIG. 7 is a graph showing the relationship between RF power and wet etch rate of the film formed on the top surface and that of the film formed on the sidewalls of the trench, showing a threshold (reference) RF power. As shown in FIG. 7, the wet etch rate of the sidewall portion decreased as RF power increased, whereas the wet etch rate of the top/bottom portions increased as the RF power increased, wherein the line representing the former and the line representing the latter intersect at an RF power of approximately 600 W. That is, the threshold RF power was approximately 600 W, and it can be understood that when RF power applied between the electrodes is higher than approximately 600 W, the top/bottom portions of the film can be removed selectively relative to the sidewall portion of the film, whereas when RF power applied between the electrodes is lower than approximately 600 W, the sidewall portion of the film can be removed selectively relative to the top/bottom portions of the film.

Further, prior to the wet etching, the top portion of the film was subjected to additional analyses: Si—N peak intensity and density. FIG. 12 is a graph showing the relationship between RF power and Si—N peak intensity [au] of the SiN film. FIG. 13 is a graph showing the relationship between RF power and density [g/cm³] of the SiN film. As can be seen from FIGS. 12 and 13, contrary to common technological knowledge (i.e., when increasing RF power, densification of the film occurs), asymmetrical plasma bombardment to the SiN film broke Si—N bonds when RF power increased, and as a result of dissociation of Si—N bonds, the density of the film decreased (the density is typically in a range of 2.6 to 3.2 g/cm³), wherein the density of a film portion to be removed by wet etching is lower than that of a film portion to remain through wet etching).

Example 2

The SiN films were deposited under the conditions shown in Table 5, where the threshold RF power was determined to be approximately 400 W in the same manner as in Example 1. The SiN films were then subjected to wet etching under the conditions shown in Table 5. FIG. 8 shows Scanning Transmission Electron Microscope (STEM) photographs of cross-sectional views of the silicon nitride films. As can be seen from FIG. 8, when RF power was 700 W, the top/bottom portions of the film were selectively removed by wet etching, and substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench. When RF power was 500 W, the top/bottom portions of the film were more predominantly removed than was the sidewall portion of the film by wet etching, but residual film remained on the top surface and at the bottom of the trench, whereas the sidewall portion of the film mostly remained. When RF power was 300 W, the sidewall portion of the film was more predominantly removed than were the top/bottom portions of the film by wet etching, and no residual film remained in some areas of the sidewall, whereas the top/bottom portions of the film mostly remained.

TABLE 5 Conditions for Deposition Cycle Substrate temperature 200° C. Pressure 350 Pa Precursor Bisdiethylaminosilane Precursor pulse 0.2 sec Precursor purge 3 sec Reactant N₂ Flow rate of reactant 2000 sccm (continuous) Flow rate of carrier 2000 sccm Ar gas (continuous) Flow rate of dilution 0 sccm gas (continuous) RF power (13.56 MHz) Variable for a 300-mm wafer (see FIG. 8) RF power pulse 3 sec Purge 0.1 sec Growth rate per cycle 0.02 nm/cycle (on top surface) Number of cycles 500 times (thickness of film on (10 nm) top surface) Step coverage (side/top; 30%; 30% side/bottom) Trench depth/ 100/33 width (nm) (AR = about 3) Distance between 13 mm electrodes Conditions for Wet etching Etching solution 0.05% HF Etching solution 20° C. temperature Duration of etching 4 min Etching rate Variable (see FIG. 8) (numbers are approximate)

Example 3

The SiN film was deposited in the same manner as in Example 1 except that RF power was 880 W. The SiN film was then subjected to wet etching under the same conditions as in Example 1. FIG. 9 shows a Scanning Transmission Electron Microscope (STEM) photograph of a cross-sectional view of the SiN film after the wet etching. As can be seen from FIG. 9, substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench.

Example 4 (Prophetic Example)

A SiN film is formed on a Si substrate (Φ300 mm) having trenches by PEALD in the same manner as in Example 1 except that RF power is 600 W. Thereafter, in the same reactor, the film is treated with a plasma under the conditions shown in Table 6 below, where RF power is 800 W which is higher than the threshold RF power, thereby causing damage to the top surface of the substrate and the bottom surface of the trench and degrading the film quality. After taking out the substrate from the reaction chamber, the substrate is subjected to wet etching under the conditions shown in Table 6 below.

TABLE 6 Conditions for Surface treatment Substrate temperature 400° C. Pressure 350 Pa Reactant N₂ Flow rate of 2000 sccm reactant (continuous) Flow rate of carrier 2000 sccm gas (continuous) Flow rate of dilution 0 sccm gas (continuous) RF power (13.56 MHz) for 880 W a 300-mm wafer Duration of RF 60 sec power application Distance between 15 mm electrodes Conditions for Wet etching Etching solution 0.5% HF Etching solution 20° C. temperature Duration of etching 2 min Etching rate 6 nm/min, (top/sidewall) 0.2 nm/min (numbers are approximate)

FIG. 10 illustrates a cross-sectional view of the silicon nitride film. Since a portion 52 of the film formed on a sidewall 51 of a trench formed in a substrate 51 does not receive substantial plasma bombardment, the portion 52 maintains film properties and remains after wet etching. In contrast, since a portion of the film formed on a top surface 51 b and a portion of the film formed on a bottom surface 51 a receive plasma bombardment, the portions degrade film properties and are removed after wet etching.

Example 5 (Prophetic Example)

A SiN film is formed on a Si substrate (Φ300 mm) having trenches by PEALD, one cycle of which is conducted under the conditions shown in Table 7 (deposition cycle) below using the PEALD apparatus illustrated in FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substrate is subjected to wet etching under the conditions shown in Table 7 below.

TABLE 7 Conditions for Deposition Cycle Substrate temperature 400° C. Pressure 350 Pa Precursor SiI₂H₂ Precursor pulse 0.3 sec Precursor purge 0.5 sec Reactant N₂ Flow rate of reactant 2000 sccm (continuous) Flow rate of carrier 2000 sccm N₂ gas (continuous) Flow rate of dilution 0 sccm gas (continuous) RF power (13.56 MHz) 100 W for a 300-mm wafer RF power pulse 3.3 sec Purge 0.1 sec Growth rate per 0.05 nm/cycle cycle (on top surface) Number of cycles (thickness 200 times of film on top surface) (10 nm) Trench depth/width (nm) 100/33 (AR = about 3) Step coverage (side/top; 100%; 100% side/bottom) Distance between 15 mm electrodes Conditions for Wet etching Etching solution 0.5% HF Etching solution 20° C. temperature Duration of etching 2 min Etching rate 0.3 nm/min, (top/sidewall) 2.4 nm/min (the numbers are approximate)

FIG. 11 illustrates a cross-sectional view of the silicon nitride films. Since RF power is 100 W which is lower than the threshold RF power (which is expected to be 600 W), a sidewall portion of the film is removed selectively relative to a top portion 53 b of the film and a bottom portion 53 a of the film by wet etching, wherein only the top/bottom portions 53 a, 53 b remain after the wet etching. This film can be used as a cap layer.

Example 6

SiN films were deposited under the conditions shown in Table 8, where the threshold pressure was determined to be approximately 300 Pa in a manner substantially similar to that in Example 1. The SiN films were then subjected to wet etching under the conditions shown in Table 8. FIG. 15 shows Scanning Transmission Electron Microscope (STEM) photographs of cross-sectional views of the silicon nitride films. As can be seen from FIG. 15, when the pressure was 150 Pa, the top/bottom portions of the film were selectively removed by wet etching, and substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench. When the pressure was 250 Pa, the top/bottom portions of the film were more predominantly removed than was the sidewall portion of the film by wet etching, but residual film remained on the top surface and at the bottom of the trench, whereas the sidewall portion of the film mostly remained. When the pressure was 350 Pa, the sidewall portion of the film was more predominantly removed than were the top/bottom portions of the film by wet etching, and no residual film remained in some areas of the sidewall, whereas the top/bottom portions of the film mostly remained.

TABLE 8 Conditions for Deposition Cycle Substrate temperature 450° C Bottle temperature 35° C. Showerhead temperature 200° C. Wall temperature 150° C. Inflow gas temperature 75° C. Precursor SiI₂H₂ Pressure Variable (see Fig 15) 350 Pa 250 Pa 150 Pa Reactant N₂ Flow rate of reactant 5000 sccm 2500 sccm (continuous) Flow rate of carrier 4000 sccm 2000 sccm gas (continuous) N₂ N₂ Flow rate of seal 200 SCCM N₂ gas (continuous) RF power (13.56 MHz) 990 W for a 300-mm wafer Precursor pulse 0.45 sec Precursor purge 0.50 sec RF power pulse 3.30 sec Purge 0.10 sec Growth rate per cycle 0.046 nm/cycle 0.018 nm/cyc 0.028 nm/cyc (on top surface) 500 times 265 times 500 times Number of cycles (23.1 nm) (4.76 nm) (14.2 nm) (thickness of film on top surface) Step coverage (side/top; 79%; 88% 73%; 65% 78%; 75% side/bottom) Trench depth/width (nm) 330/33 (AR = about 10) Distance between electrodes 15 mm Conditions for Wet etching Etching solution 1:100 DHF Etching solution temperature 20° C. Duration of etching 1 min Etching rate Variable (see FIG. 15) (numbers are approximate)

Example 7

SiN films were deposited under the conditions shown in Table 9, where the threshold RF power (HRF alone) was determined to be approximately 550 W in a manner substantially similar to that in Example 1. The SiN films were then subjected to wet etching under the conditions shown in Table 9. FIG. 16 shows Scanning Transmission Electron Microscope (STEM) photographs of cross-sectional views of the silicon nitride films. As can be seen from FIG. 16, when HRF power (13.56 MHz) was 880 W without LRF power, the top/bottom portions of the film were selectively removed by wet etching, and substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench. When HRF power was 550 W without LRF power, the top/bottom portions of the film and the sidewall portion of the film were about equally etched and mostly remained. When HRF power was 550 W and 50 W of LRF power (400 kHz) was added thereto, the top/bottom portions of the film were more predominantly removed than was the sidewall portion of the film by wet etching, and no residual film remained in some areas of the top/bottom, whereas the sidewall portion of the film mostly remained.

TABLE 9 Conditions for Deposition Cycle Substrate temperature 450° C. Bottle temperature 35° C. Showerhead temperature 200° C. Wall temperature 150° C. Inflow gas temperature 75° C. Precursor SiI₂H₂ Pressure Variable (see FIG. 16) Reactant N₂ Flow rate of reactant 5000 sccm (continuous) Flow rate of carrier 2000 sccm N₂ gas (continuous) Flow rate of seal 200 sccm N₂ gas (continuous) RF power (13.56 MHz) 550 W 550 W 880 W for a 300-mm wafer RF power (400 kHz) 0 W 50 W 0 W for a 300-mm wafer (None) (None) Precursor pulse 0.30 sec 0.30 sec 0.30 sec Precursor purge 1.00 sec 1.00 sec 0.5 sec RF power pulse 3.30 sec 3.30 sec 3.30 sec Purge 0.10 sec 0.10 sec 0.10 sec Growth rate per cycle 0.038 0.052 0.045 (on top surface) nm/cycle nm/cycle nm/cycle Number of cycles 300 times 300 times 430 times (thickness of film (11.3 nm) (15.5 nm) (19.6 nm) on top surface) Step coverage (side/top; 73%; 68.% 73%; 68.% 67%; 77% side/bottom) Trench depth/width (nm) 100/33 (AR = about 3) Distance between 12 mm 12 mm 15 mm electrodes Conditions for Wet etching Etching solution 1:100 DHF Etching solution 20° C. temperature Duration of etching 5 min Etching rate Variable (see FIG. 16) (numbers are approximate)

Example 8

SiN films were deposited under the conditions shown in Table 10, where the threshold RF power (HRF alone) was determined to be approximately 400 W in a manner substantially similar to that in Example 1. The SiN films were then subjected to wet etching under the conditions shown in Table 10. FIG. 17 shows Scanning Transmission Electron Microscope (STEM) photographs of cross-sectional views of the silicon nitride films. As can be seen from FIG. 17, when HRF power (13.56 MHz) was 200-250 W without LRF power, the sidewall portion of the film was selectively removed by wet etching, and substantially no film remained (no residual film was observed) on the sidewall surface of the trench. When LRF power (430 kHz) was 300 W without HRF power, the top/bottom portions of the film were selectively removed by wet etching, and substantially no film remained (no residual film was observed) on the top surface and at the bottom of the trench, whereas the sidewall portion of the film mostly remained.

TABLE 10 Conditions for Deposition Cycle HRF power (13.56 MHz) 200-250 W 0 W for a 300-mm wafer LRF power (430 kHz) 0 W 300 W for a 300-mm wafer Substrate temperature 450° C Pressure 10 Torr 4 Torr Precursor DCS Reactant NH₃ Flow rate of reactant 50 sccm (continuous) Flow rate of carrier 1,000 sccm Ar gas (continuous) Flow rate of dilution 500 SCCM N₂, gas (continuous) 2,000 sccm Ar Precursor pulse 0.5 sec Precursor purge 1.0 sec Reactant pulse w/o RF plasma 0.5 sec RF power pulse 2.0 sec Purge 0.5 sec Growth rate per cycle (on 0.73 Åmin >0.73 Å/min top surface) Number of cycles (thickness 480 times of film on top surface) (445 nm) Step coverage (side/top; 70%; 70% side/bottom) Non-uniformity in film 3.73% 0.86% thickness within wafer surface Trench depth/width (nm) 100/33 (AR = about 3) Distance between electrodes 10 mm Conditions for Wet etching Etching solution DI:HF = 100:1 Etching solution temperature Room temperature Duration of etching >0.5 min Etching rate Variable (see FIG. 17) (numbers are approximate)

Example 9

As shown in FIG. 17, by manipulating a ratio of HRF/LRF, reverse topological selectivity (RTS) can effectively be accomplished. The reason that the top/bottom portions of the film were selectively removed by wet etching when the LRF power was used appears to reside in the amount of impurities such as hydrogen contained in the resultant film. It appears that the LRF power process generated more hydrogen radicals than did the HRF power process and provided more hydrogen atoms to the film, increasing the wet etch rate. Table 11 below shows the hydrogen content of the SiN films deposited on the blanket (flat) wafer in the same manner as in Example 8. As shown in Table 11, the SiN film formed by the LRF power process contained more hydrogen atoms than the SiN film formed by the HRF power process, resulting in higher WER in the SiN film by the LRF power process than that by the HRF power process. Accordingly, it can be understood that the hydrogen content in the film is one of the main factors of the RTS.

TABLE 11 Hydrogen WER to content (at. %) thermal oxide HRF (13.56 MHz, 21.0 at. % 1.30 200 W) LRF (430 KHz, 26.2 at. % 6.31 300 W) (numbers are approximate)

Example 10 (Prophetic Example)

As shown in Example 2 (FIG. 8), by manipulating RF power (HRF), reverse topological selectivity (RTS) can effectively be accomplished. Also, as shown in FIG. 17, by manipulating a ratio of HRF/LRF, reverse topological selectivity (RTS) can effectively be accomplished. In the wet etching step following the deposition step, as an etching solution (etchant solution), not only a hydrogen fluoride (HF) but also phosphoric acid (H₃PO₄) or any other suitable solution can be used for accomplishing RTS. However, the type of etching solution can affect the degree of RTS. For example, Table 12 shows that the etching rates at a top surface and at sidewalls of a trench vary depending on the type of etchant solution, wherein the deposited dielectric film is formed in a manner similar to that in Example 2 or Example 8.

TABLE 12 Etchant Top Side solution (nm/min) (nm/min) Film profile BHF130* 2 0.5 Similar to “700 W” in FIG. 8 or “LRF” in FIG. 17 0.2 5 Similar to “300 W” in FIG. 8 or “HRF” in FIG. 17 70° C.-H₃PO₄ 4 0 Similar to “700 W” in FIG. 8 or “LRF” in FIG. 17 0.2 5 Similar to “300 W” in FIG. 8 or “HRF” in FIG. 17 *Manufactured by Daikin Industries, Ltd., Japan (a hydrogen fluoride containing 5% ammonium hydrogen fluoride, 37% ammonium fluoride, and 58% water) (numbers are approximate)

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We claim:
 1. A method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate, comprising: (i) simultaneously forming a dielectric film containing a Si—N bond on the upper surface and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage in a reaction space between two electrodes between which the substrate is placed in parallel to the two electrodes; (ii) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by etching which removes the one of the top/bottom portion and the sidewall portion of the dielectric film more predominantly than the other according to the different chemical resistance properties; and (iii) obtaining a reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the plasma in step (i) is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes, wherein plasma density is higher than the reference plasma density, wherein the etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film, wherein obtaining the reference plasma density comprises performing the forming of dielectric films as recited in step (i), then determining the chemical resistance property by etching as recited in step (ii), then repeating these steps for a plurality of times using different plasma density values, then obtaining the reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, and wherein the dielectric film is a SiN film.
 2. The method according to claim 1, wherein in step (i), the dielectric film is formed by plasma-enhanced atomic layer deposition (PEALD).
 3. The method according to claim 1, wherein the plasma is a plasma of Ar, N₂, or O₂.
 4. The method according to claim 1, wherein in step (i), a halogenated silane is used as a precursor.
 5. The method according to claim 1, wherein the etching is the wet etching, which is conducted using a solution of hydrogen fluoride (HF) or phosphoric acid.
 6. A method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate, comprising: (i) simultaneously forming a dielectric film containing a Si—N bond on the upper surface and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage in a reaction space between two electrodes between which the substrate is placed in parallel to the two electrodes; (ii) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by etching which removes the one of the top/bottom portion and the sidewall portion of the dielectric film more predominantly than the other according to the different chemical resistance properties; and (iii) obtaining a reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the plasma in step (i) is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes, wherein plasma density is higher than the reference plasma density, wherein the etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film, wherein obtaining the reference plasma density comprises performing the forming of dielectric films as recited in step (i), then determining the chemical resistance property by etching as recited in step (ii), then repeating these steps for a plurality of times using different plasma density values, then obtaining the reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the plasma density is modulated by tuning the pressure in the reaction space, wherein the plasma density increases by lowering the pressure.
 7. The method according to claim 6, further comprising, prior to steps (i) and (ii), repeating the following steps to determine the reference plasma density: simultaneously forming a dielectric film under the same conditions as in step (i) except that the pressure is changed as a variable; and substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by etching under the same conditions as in step (ii).
 8. The method according to claim 6, wherein the pressure in step (i) is controlled below 300 Pa.
 9. A method for fabricating a layer structure constituted by a dielectric film containing a Si—N bond in a trench formed in an upper surface of a substrate, comprising: (i) simultaneously forming a dielectric film containing a Si—N bond on the upper surface and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the dielectric film formed on the upper surface and the bottom surface and a sidewall portion of the dielectric film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage in a reaction space between two electrodes between which the substrate is placed in parallel to the two electrodes; (ii) substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by etching which removes the one of the top/bottom portion and the sidewall portion of the dielectric film more predominantly than the other according to the different chemical resistance properties; and (iii) obtaining a reference plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the plasma in step (i) is a capacitively coupled plasma (CCP) which is excited by applying RF power to one of the two electrodes, wherein plasma density is higher than the reference plasma density, wherein the etching in step (ii) removes the top/bottom portion of the dielectric film selectively relative to the sidewall portion of the dielectric film, wherein obtaining the reference plasma density comprises performing the forming of dielectric films as recited in step (i), then determining the chemical resistance property by etching as recited in step (ii), then repeating these steps for a plurality of times using different plasma density values, then obtaining the reference ion plasma density at which the chemical resistance properties of the top/bottom portion of the dielectric film and the sidewall portion of the dielectric film are substantially equivalent, wherein the plasma density is modulated by tuning a ratio of high frequency RF power to low frequency RF power constituting the RF power, wherein the plasma density increases by decreasing the ratio, wherein the high-frequency RF power has a frequency of 1 MHz or higher and the low-frequency RF power has a frequency of less than 1 MHz.
 10. The method according to claim 9, further comprising, prior to steps (i) and (ii), repeating the following steps to determine the reference plasma density: simultaneously forming a dielectric film under the same conditions as in step (i) except that the ratio is changed as a variable; and substantially removing either one of but not both of the top/bottom portion and the sidewall portion of the dielectric film by wet etching under the same conditions as in step (ii).
 11. The method according to claim 9, wherein the ratio of high frequency RF power to low frequency RF power is 0/100 to 95/5.
 12. The method according to claim 11, wherein the RF power consists of the low frequency RF power.
 13. The method according to claim 1, wherein no annealing is conducted between steps (i) and (ii). 